Vulnerability

CVE-2021-42321

High· 8.8KEVEXPLOITCVSS8.8EPSS94%

.rules3/5

Microsoft Exchange Server Remote Code Execution Vulnerability

An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.

Threat signal

100/100

Severe

Severity

high

CVSS

8.8

EPSS

94%

Active

KEV

CISA KEV — actively exploited

Ransomware: Known1655d overdue

AffectedMicrosoft — Exchange

Added to KEV

2021-11-17

Federal patch due (BOD 22-01)

2021-12-01

Required action (CISA verbatim)

Apply updates per vendor instructions.

Vendor advisory + references

https://nvd.nist.gov/vuln/detail/CVE-2021-42321

CISA description: “An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.”

CVSS

v3.1Open in FIRST calculator →

8.8/ 10HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack VectorNetworkExploitable remotely over the internet — no local access needed.
Attack ComplexityLowNo special conditions — exploit works reliably.
Privileges RequiredLowStandard user privileges sufficient.
User InteractionNoneFully automated — no victim action needed.
ScopeUnchangedImpact contained to the vulnerable component.
Confidentiality ImpactHighTotal disclosure of sensitive data.
Integrity ImpactHighTotal compromise of integrity — full data modification possible.
Availability ImpactHighTotal loss of availability — full DoS possible.

EPSS

Exploit prediction · 30-day horizonFIRST.org →

93.6%

probability of exploitation in next 30 days

p100

higher than 100% of all CVEs

3-day trend↑ 0pp

Statistically about to be weaponized — top-tier triage urgency.

Vendor VEX

No VEX statements published for CVE-2021-42321. Vendors publish VEX (Vulnerability Exploitability eXchange) to assert per-product whether a CVE is actually exploitable in their distribution.

SSVCAct

Active exploitation with total impact on essential/support systems

exploitation: active
automatable: yes
impact: total
mission: support

Lifecycle

2021-11-17Added to CISA KEVransomware: Known
2021-11-17Public exploit observedmetasploit
2021-11-17Published
2021-12-01Federal patch due (BOD 22-01)
2026-06-12Last modified1 source

No source-event history recorded yet. New revisions will appear here as ingestors re-fetch this CVE.